This invention relates to a plasma process apparatus for generating plasma of a process gas to perform etching, ashing, film forming, etc. of a to-be-treated object such as a semiconductor wafer.
An etching apparatus has been proposed in which upper and lower electrodes are opposed to each other within a process chamber defined in an airtight process container. In this apparatus, after a to-be-treated object, for example, a semiconductor wafer is fixed on a mount surface or upper surface of the lower electrode, a predetermined process gas is introduced into the process chamber, and a predetermined high frequency power is applied to each of the upper and lower electrodes to excite the process gas into plasma, thereby performing predetermined etching of the object.
Japanese Patent Application KOKAI Publication No. 4-38132, for example, has recently proposed an etching apparatus in which mount surfaces are formed at both the upper and lower electrodes for fixing to-be-etched objects thereon. This apparatus can treat two or more objects simultaneously, which means that it can achieve a high throughput.
In the etching apparatus in which the mount surface is provided on the lower electrode only, that surface of the upper electrode which is opposed to the lower electrode is exposed to the atmosphere of plasma and hence easily etched during the etching process. Accordingly, the upper electrode must be exchanged with a new one in a relatively short time, which inevitably leads to an increase in the operation cost of the etching apparatus and to a reduction in throughput due to a time loss during the exchange.
On the other hand, in the etching apparatus in which both the upper and lower electrodes have their respective mount surfaces, those surfaces of the electrodes which are opposed to each other are covered with to-be-treated objects mounted thereon during the etching process, and therefore not easily etched. Therefore, the time of electrode exchange can be prolonged. Moreover, since in this apparatus, two objects can be simultaneously treated as aforementioned, it can realize a high throughput. However, to generate uniform plasma near the objects fixed on the mount surfaces has been very difficult so far. It is now considered one of the to-be-overcome technical matters to generate uniform plasma near the to-be-treated surface of each object and apply plasma of a desired state to the to-be-treated surface, in order to perform a desired uniform process of it.